useMemo docs state that value will be computed when a new functions instance is passed which is not true

[DimitarNestorov]

The docs say that

a new value will be computed whenever a new function instance is passed as the first argument

The following code shows otherwise. The function instance is always the same, however a new value for n is computed on every render because no array is passed.

import React, { useMemo, useState } from "react";
import ReactDOM from "react-dom";

class RandomNumberContainer {
  number = Math.random();
}

function createRandomNumberContainer() {
  return new RandomNumberContainer();
}

function App() {
  const [i, setI] = useState(0);
  const n = useMemo(createRandomNumberContainer);
  const n2 = useMemo(createRandomNumberContainer, []);

  return (
    <div className="App">
      <p>i: {i}</p>
      <p>number: {n.number}</p>
      <p>number2: {n2.number}</p>
      <button onClick={() => setI(i + 1)} />
    </div>
  );
}

const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);

Here's an example sandbox: https://codesandbox.io/s/4x68k8nrw

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[gaearon]

You're right. :-( This behavior changed from alphas to stable but we missed this during the docs update. Sorry.